1. Field of the Invention
The present invention relates to an improved muffler for an internal combustion engine.
2. Description of the Prior Art
In general, a muffler is connected at an outlet of an exhaust gas system of an internal combustion engine to reduce exhaust sound in an internal combustion engine. Such muffler has resistance to an exhaust gas flow to increase backpressure of the internal combustion engine and to reduce an output of the engine. Therefore, it has been desired to obtain a muffler having smaller pressure loss and higher muffler effect.
The muffler shown in FIG. 1 has been known. FIG. 1 is a schematic sectional view of a conventional muffler. In FIG. 1, the reference (1) designates a casing of the muffler: (a) to (c) respectively designate partition plates for dividing an internal space of the casing (1) into a plurality of compartments; (2) designates an inlet pipe which pass through the partition plates (a) to (c) to open in a space surrounded by the casing and the partition plate (c); (d) to (f) respectively communication pipes for connecting the spaces formed by the casing (1) and the partition plates (a), (b), (c); and (2') designates an outlet pipe one end of which is opened in a space surrounded by the casing (1) and the partition plate (a) and the other end of which is opened in the atmosphere.
In the muffler having the structure as shown by the arrow lines, the exhaust gas discharged from the engine is fed through the inlet pipe (2) into the space surrounded by the casing (1) and the partition plates (c) and is passed through the communication pipe (e) into the space surrounded by the casing (1) and the partition plates (a), (b) and is further fed through the communication pipe (d) into the space surrounded by the casing (1) and the partition plates (b), (c) and then, is fed through the communication pipe (f), the space surrounded by the casing (1) and the partition plate (a) and outlet pipe to the atmosphere. On the other hand, the exhaust sound leaked from the engine together with the exhaust gas is also discharged through the same passage to the atmosphere. During the steps of alternating propagation of the sound through the communication pipes (d), (e), (f) and the spaces surrounded by the casing (1) and the partition plates (a), (b), (c), sound energy density as a sound energy per unit area is reduced by expansion of sound wave in each space whereas the sound energy fed through each communication pipe to the next space is reduced. In such steps, the exhaust sound leaked from the outlet pipe (2') to the atmosphere is reduced. In the conventional muffler, however, the gas flow system in the muffler causes serious reduction and expansion of the sectional areas to increase the gas flow resistance whereby the back-pressure of the engine is increased and the output of the engine and the efficiency are disadvantageously reduced. The exhaust gas flow complicated gas passages whereby the flow momentum change is large to cause turbulent flow and the aerodynamic sound is secondarily resulted in the inside of the muffler to reduce the muffler effect. In such muffler, as well known, resonance phenomenon is easily caused to remarkably reduce the muffler effect in specific frequency regions. When the revolution speed of the engine is remarkably changed, it is indispensable to coincide the spectral frequency of the exhaust sound with the resonance frequency in specific revolution speed, whereby the muffler effect is remarkably reduced. These disadvantages have been found.
In order to overcome the disadvantages of the conventional muffler, it is necessary to linearly arrange the gas passage in the muffler to reduce the pressure loss. In order to attain a desired muffler effect in the linear arrangement of the gas passage in the muffler, it is necessary to use a sound absorber. The exhaust sound usually has spectral sounds in broad frequency regions. Thus, it is desired to use a sound absorber having sound absorbability in broad frequency region and accordingly, a porous sound absorber is preferably used. Thus, the exhaust gas contains tar and soot and the sound absorber causes clogging by adhering the tar and soot on the surface of the porous sound absorber and the sound is not passed through the sound absorber to remarkably reduce the sound absorbability. Therefore, in the equipment of the sound absorber in the muffler, it is necessary to prevent the clogging of the sound absorber caused by the adhesion of the tar and soot on the surface of the sound absorber.